Natural fats and oils have various undesirable components such as metals, free fatty acids and phospholipids and therefore have to be refined. In the refining of natural fats and oils, a distinction is made between physical and chemical refining.
In the case of chemical refining, which is used predominantly for triglyceride oils having a low fraction of free fatty acids, the free fatty acids are separated off by reaction with a base. So-called soapstocks are formed in this case, an aqueous mixture of base, free fatty acids, the salts of the free fatty acids and also oil. These soapstocks are an undesired by-product of chemical refining which are of low value and limited use.
In the case of physical refining, which is used predominantly for triglyceride oils having a relatively high fraction of free fatty acids, the free fatty acids are in contrast separated off thermally. In this way, the formation of soapstocks may be avoided, but at the same time high temperatures (up to 260° C.) have to be applied in order to be able to separate off the free fatty acids from the oil by distillation.
In addition to chemical and physical refining, other methods are described in the prior art by which free fatty acids may be separated off or soapstocks may be processed. For example, liquid-liquid extraction techniques are used here (C. E. C. Rodrigues, C. B. Gonçalves, E. Batista, J. A. Meirelles, Recent Patents on Engineering 2007, 1, 95-102).
WO 2016/149692 A1 describes the acidification of aqueous solutions which originate from saponification reactions and comprise lipids. The lipid-containing raw material is mixed with base (especially sodium or potassium hydroxide) and saponified. CO2 is then injected, reacted with the reaction mixture and the aqueous phase is removed.
In addition, U.S. Pat. No. 2,771,480 also describes the regeneration of fatty acids by means of ion exchangers. This, however, is very costly.
CN 106281672 A describes the treatment of triglyceride oils with antioxidants (e.g. tocopherol, lactate) and alkali metal salts thereof for removing trichloropropanol and derivatives thereof.
WO 2012/031176 A1, WO 2016/189114 A1, WO 2016/189115 A1 and WO 2016/189328 A1 describe the treatment of triglyceride oils with quaternary ammonium salts and solutions thereof for removing free fatty acids, metals and other undesirable components.
In WO 2016/189114 A1, a triglyceride oil is extracted with an aqueous solution of a basic quaternary ammonium salt in order to remove fatty acids therefrom. After extraction, the phases are separated. To regenerate the aqueous solution, which is necessary in order to be able to use this in a new extraction step of the process, this aqueous phase, charged with fatty acid salts from the triglyceride oil, is pressurized with CO2. Free fatty acids are formed from the fatty acid salts as a result, which may be separated off from the aqueous phase.
Although WO 2016/189114 A1 discloses a reliable method for extracting free fatty acids from triglyceride oils, this method has a problem, especially in industrial scale applications. Quaternary ammonium salts are surface-active and are frequently used as cationic surfactants in soaps and fabric softeners. Their removal after treatment of triglyceride oils is therefore technically very demanding right from the start since they emulsify with water and oil and complicate the phase separation. The quaternary ammonium salts used in the extraction of the fatty acids from the triglyceride oil can therefore only be removed with difficulty, or not completely removed, from the triglyceride oil.
This is especially disadvantageous when using the extracted triglyceride oils as edible oils: not only are some quaternary ammonium salts of concern to health, quaternary ammonium salts, and especially choline, also have the tendency to a foul smell and sometimes even dark-colored deposits. This causes a distinct reduction in quality of the extracted oil. It is therefore desirable to further improve the extraction technique of the prior art (e.g. WO 2016/189114 A1).
It is therefore an object of the present invention to provide a process for extracting fatty acids from triglyceride oils which does not have the aforementioned disadvantages.
Above all, a process should be provided which allows reuse of the phases and at the same time ensures high quality of the extracted triglyceride oil.